1. Field of the Invention
The present invention relates to a method of detecting an end point of polishing. The detection is performed such that a wafer having a permalloy magnetic layer constituted by forming a permalloy magnetic layer made of permalloy containing metal, such as iron, nickel or cobalt, such as Ni--Fe, Mn--Fe, Co--Fe Ni--Rh--F, Co--Zr--Fe, Co--Fe--B, on the surface of a substrate made of silicon, an alumina-titanium carbide (AlTiC) alloy or glass and having a circuit made of Cu, Ag or Au formed if necessary and furthermore incorporating an insulating layer made of aluminum oxide or the like is joined to a chuck. Then, the wafer is pressed against a platen having a polishing cloth or a lapping surface plate (hereinafter the platen and the lapping surface plate are generally called a "polishing surface plate" and a CMP polishing apparatus and a lapping apparatus are generally called a "CMP polishing apparatus") made of copper, tin, aluminum or plastic. While supplying abrasive material slurry to the surface of the polishing surface plate, the polishing surface plate and the wafer are rotated to polish the insulating layer to perform chemimechanical polishing (CMP) until the permalloy layer is exposed to the outside. As an alternative to this, the wafer is sucked to a chuck table by using a vacuum to downwards and then a platen to which a polishing cloth is bonded, namely a polishing pad, is pressed against the upper surface of the wafer. While supplying abrasive material slurry to the platen or supplying abrasive material slurry to the upper surface of the wafer, the platen and the wafer are rotated to polish the insulating layer to perform chemimechanical polishing (CMP) until the permalloy layer is exposed. The present invention also relates to an apparatus for detecting an end point of polishing.
2. Description of the Related Art
For example, a magnetic recording head substrate is, as shown in FIGS. 2A to 2D, manufactured such that a permalloy layer 3 is formed on a substrate 2. Then, a wafer 1 (see FIG. 2A) having an aluminum insulating layer formed thereon is polished by chemimechanical polishing (CMP) until the permalloy layer is exposed to the outside (see FIG. 2D). Also the CMP polishing operation is performed when a device wafer is manufactured as a substitute for the magnetic head substrate. At this time, a structure consisting of 2 to 10 permalloy layers and device layers is sometimes constituted.
When the water is polished as described above, automatic polishing free of no manpower is required from the market. A variety of pieces of automatic CMP apparatus for automatically detecting an end point of polishing have been suggested.
The end point of polishing is detected by any one of the following methods.
(1) A method for determining the end point in accordance with an amount of polishing by measuring a change of the thickness of the wafer which is being polished by a thickness meter (refer to Japanese Patent Laid-Open No. 62-257742, Japanese Patent Laid-Open No. 9-193003, Japanese Patent Laid-Open No. 10-106984 and Japanese Patent Laid-Open No. 10-98016). PA1 (2) A method for determine the end point in accordance with a load electric current, voltage or change in the resistance of the motor which rotates the platen or the chucking mechanism during the polishing operation (refer to Japanese Patent Laid-Open No. 61-188702, Japanese Patent Laid-Open No. 6-252112, Japanese Patent Laid-Open No 8-99625, Japanese Patent Laid-Open No. 9-70753, Japanese Patent Laid-Open No. 10-44035, Japanese Patent Laid-Open No. 10-128658 and Japanese Patent Laid-Open No. 10-177976). PA1 (3) A method determining the end point of polishing in accordance with change in the torque of the motor which rotates the platen or the chucking mechanism during the polishing operation (refer to Japanese Patent Laid-Open No. 5-138529, Japanese Patent Laid-Open No. 6-216095, Japanese Patent Laid-Open No. 8-139060, Japanese Patent Laid-Open No. 8-197417, Japanese Patent Laid-Open No. 9-36073, Japanese Patent Laid-Open No. 9-262743 and Japanese Patent Laid-Open No. 10-256209). PA1 (4) A method in which the wafer being polished is irradiated with a laser beam to determine the end point of polishing in accordance with the quantity of reflected light (refer to Japanese Patent Laid-Open No. 57-138575, Japanese Patent Laid-Open No. 61-214970, Japanese Patent Laid-Open No. 4-255218, Japanese Patent Laid-Open No. 5-309559, Japanese Patent Laid-Open No. 7-328916, Japanese Patent Laid-Open No. 8-174411 Japanese Patent Laid-Open No. 9-7985 and Japanese Patent Laid-Open No. 10-160420). PA1 (5) A method with which a color sensor is disposed opposite to a chuck for holding a device substrate which has an interlayer insulating film on which a metal film has been formed to detect the color of the interlayer insulating film which has been chemimechanically polished (refer to JP-A-11-70467). PA1 (6) A method in which phosphorus or tracer particles serving as an index is added to the polishing-material slurry to measure the quantity of the index on the polishing cloth so as to determine the end point of polishing (refer to Japanese Patent Laid-Open No. 2-241017 and Japanese Patent Laid-Open No. 8-69987).
The method (1) in which the thickness of the wafer is measured is arranged such that the thickness of only a part of the wafer is measured. Since a long time is required to measure the distribution of thicknesses of the overall portion of the wafer, only a poor accuracy can be realized.
Each of the determining method (2) in which the electric current, the voltage or the resistance is used and the method (3) in which the torque is used, is not a method of directly observing the surface of the polished wafer. Also only a poor accuracy of flattening can be obtained.
The method (4) in which the quantity of reflected laser beam is used, is arranged such that the wafer is directly irradiated with the laser beam to determine the end point in accordance with the quantity of reflected light. Therefore, presence of water of the polishing-material slurry for use in the CMP polishing process on the surface of the wafer causes data to be scattered. Hence it follows that an apparatus for cleaning and drying the position on the surface of the wafer on which the laser beam is made incident and from which the same is reflected must be joined. Therefore, the foregoing method cannot be employed when the size of the CMP apparatus is reduced. What is worse, the cost of the apparatus cannot be reduced. Moreover, the polishing process is interrupted because the cleaning and drying processes of the wafer have to be performed. The method (5) with which the color sensor is employed is free of description about a specific embodiment (computer soft program) of detecting the end point of polishing. Moreover, it is difficult to instantaneously observe the overall surface of the device wafer by one color sensor when a consideration is made from the disclosed drawings. Therefore, the method cannot be employed from a viewpoint of practical use.
The method (5) in which the index is added cannot be employed because the index's influences on polishing of the wafer and on a post-process performed after the CMP polishing process has been completed are not known.